We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ({tilde t}1) in 5.4 ± 0.3 fb−1 of data from the D0 detector at a p{bar p} center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino ({tilde {nu}}), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected and new exclusion limits at the 95% C.L. are set for a portion of the (m{sub {tilde t}1}, m{sub {tilde {nu}}}) mass plane.

We report the result of a search for the pair production of the light top squark decaying to two bottom quarks, an electron, a muon, and two sneutrinos in 3.1 ±0.19 fb−1 of data from the DO detector at the Tevatron, Fermilab's (square root)s = 1.96 TeV p {bar p} collider. No significant excess of events above the standard model prediction was detected and new exclusion limits at the 95% confidence level have been set for a portion of the stop mass-sneutrino mass plane.

We present the results of a search for pair production of the supersymmetric partner of the top quark (the stop quark ≈1) decaying to a b-quark and a chargino {tilde {chi}}1{sup {+-}} with a subsequent {tilde {chi}}1{sup {+-}} decay into a neutralino {tilde {chi}}1°, lepton l, and neutrino [nu]. Using a data sample corresponding to 2.7 fb−1 of integrated luminosity of p{bar p} collisions at √s = 1.96 TeV collected by the CDF II detector, we reconstruct the mass of candidate stop events and fit the observed mass spectrum to a combination of standard model processes and stop quark signal. We find no evidence for {tilde t}1{bar {tilde t}}1 production and set 95% C.L. limits on the masses of the stop quark and the neutralino for several values of the chargino mass and the branching ratio [Beta]({tilde {chi}}1{sup {+-}} → {tilde {chi}}1°l{sup {+-}}[nu]).

Abstract: A search for new phenomena with top quark pairs in final states with one isolated electron or muon, multiple jets, and large missing transverse momentum is performed. Signal regions are designed to search for two-, three-, and four-body decays of the directly pair-produced supersymmetric partner of the top quark (stop). Additional signal regions are designed specifically to search for spin-0 mediators that are produced in association with a pair of top quarks and decay into a pair of dark-matter particles. The search is performed using the Large Hadron Collider proton-proton collision dataset at a centre-of-mass energy of s√ = 13 TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb−1. No significant excess above the Standard Model background is observed, and limits at 95% confidence level are set in the stop-neutralino mass plane and as a function of the mediator mass or the dark-matter particle mass. Stops are excluded up to 1200 GeV (710 GeV) in the two-body (three-body) decay scenario. In the four-body scenario stops up to 640 GeV are excluded for a stop-neutralino mass difference of 60 GeV. Scalar and pseudoscalar dark-matter mediators are excluded up to 200 GeV when the coupling strengths of the mediator to Standard Model and dark-matter particles are both equal to one and when the mass of the dark-matter particle is 1 GeV

A search for pair production of the lightest supersymmetric partner of the top quark, {tilde t}1, is performed in the lepton+jets channel using 0.9 fb−1 of data collected by the D0 experiment. Kinematic differences between {tilde t}1{bar {tilde t}}1 and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark ({tilde t}1 → {tilde {chi}}1 b) are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.